Maybe it's the same mechanism. We haven't evolved a way to cope with the intense pleasure of artificial foods such as ice cream and so it can spawn a misdirected survival drive in the same way that drink/drugs can. Or perhaps the sugar Beast is just our old friend wearing a different hat - a sugar rush may not be it's first choice of buzz but it's something at least.
Perhaps a purist would say that there's also a 'fit Beast' because of the buzz from exercise - the runners high for example. The body probably isn't meant to be athletically fit. But just as there's 'good' selfishness, such as assertiveness and a proper level of self-regard and self-care, as well as 'bad' selfishness, perhaps there's also a good buzz as well as a bad.